Conventionally, printed materials in each of which images are printed on both sides of a base member have been widely used for advertisements, decorations, and the like. In a process of printing images on a front surface and a back surface of the base member, normally, after an image is printed on one of the surfaces, the base member is reversed and another image is printed on the other surface. For this reason, it is not possible to produce a printed material with high efficiency. Further, when it is intended to print images on both sides of a web-like base member, it is difficult to perform alignment of a plurality of images on a front surface and a plurality of images on a back surface.
Then, proposed is a technique in which two images are printed to be stacked on one of main surfaces of a transparent base member. Japanese Patent Application Laid Open No. 2010-5878 (Document 1) discloses a printed material in which a first layer, a second shielding layer, and a third layer are stacked in this order on one surface of a transparent film by an ink jet printer. The first layer and the third layer are formed of color ink and the second shielding layer is formed of white ink. In the printed material, by forming the second shielding layer, it is possible to prevent the third layer from being seen through when the first layer is visually recognized, and it is similarly possible to prevent the first layer from being seen through when the third layer is visually recognized. U.S. Patent Application Publication No. 2006/0158473 (Document 2) also discloses a printed material in which a first image, a white ink layer, and a second image are formed in this order on one surface of a transparent base member.
In a case where an image is printed on a transparent base member, since the amount of applied ink (the application amount of ink) varies with the gray level, there appears micro-undulation on a surface of the image depending on the kind of ink. As shown in Documents 1 and 2, in the techniques in which a plurality of image layers are stacked on one surface of the transparent base member, the undulation of the first image layer formed on a main surface of the transparent base member appears in the second image layer indirectly stacked on the first image layer. In a case where image layers are formed by discharging ultraviolet curable ink, particularly, the undulation of the first image layer becomes larger.